Fetal heartbeat monitoring system with plural transducers in one plane and at different angles thereto

ABSTRACT

Fetal heartbeat monitoring system in which a plurality of ultrasonic beams are transmitted at different angles into the uterus of an expectant mother. A plurality of receiving transducers are inclined at different angles for receiving the signal as it is reflected from the fetus and/or uterus walls, the frequency of the reflected signal differing from that of the transmitted signal by an amount corresponding to the rate of the fetal heart motion. A system of rate computation from the resultant doppler fetal heart motion signal is employed which utilizes frequency domain techniques. The heart rate signal is extracted from the doppler heart motion signal by means of a diode demodulator and low frequency band pass filter.

United States Patent [191 Goldberg 1 Dec. 25, 1973 FETAL HEARTBEATMONITORING SYSTEM WITH PLURAL TRANSDUCERS IN ONE PLANE AND AT DIFFERENTANGLES THERETO [75] Inventor: Paul R. Goldberg, East Palo Alto,

[21] Appl. No.: 120,970

[52] US. Cl. l28/2.05 T, l28/2.05 Z [51] Int. Cl.; A6lb 5/02 [58] Fieldof Search 128/2 V, 2.05 A,

128/2.05 F, 2.05 M, 2.05 O, 2.05 R, 2.05 S, 2.05 T, 2.05 Z, 24 A3,283,181 11/1966 Johanson 128/2.05 S 3,577,772 5/1971 Perilha et al128/2 V 3,587,561 6/1971 Ziedonis....' 128/2.05 R

Primary Examiner-William E. Kamm Attorney-Flehr, Hohbach, Test,Albritton & Herbert 5 7 ABSTRACT Fetal heartbeat monitoring system inwhich a plurality of ultrasonic beams are transmitted at differentangles into the uterus of an expectant mother. A plurality of receivingtransducers are inclined at different angles for receiving the signal asit is reflected from the fetus and/or uterus walls, the frequency of thereflected signal differing from that of the transmitted signal by anamount corresponding to the rate of the fetal heart motion. A system ofrate computation from the resultant doppler fetal heart motion signal isemployed which utilizes frequency domain techniques. The heart 5References Cited rate signal is extracted from the doppler heart motionUNITED STATES PATENTS signal by means of a diode demodulator and lowfre- 3,56l,430 2/1971 0 Filler, Jr. et al. 128/2.05 R quency band passfilter 3,237,623 3/1966 Gordon 128/24 A 5 Claims, 13 Drawing Figures 28M [MHZ /'/7 76 050444702 A9 2 72 29 f 8 f f 73 PF D005 flue/a {4 A maDEMODULATOP AMP. I 6/ 6% FeiousA/cr 90AM, fins/m2 691mm:

PM? [OM/aw Dupe/w Pscoe ie FETAL HEARTBEAT MONITORING SYSTEM WITH PLURALTRANSDUCERS IN ONE PLANE AND AT DIFFERENT ANGLES TI-IERETO BACKGROUND OFTHE INVENTION This invention pertains generally to systems and methodsfor monitoring fetal heartbeats and more particularly to a fetalheartbeat detector ultilizing ultrasonics and the Doppler principle. 7

In recent years, members of the medical profession have recognized thedesirability of being able to monitor the heartbeat of a fetus withoutinvasion of the mothers body. Such monitoring is particularly valuablesince it provides an early warning of disorders such as fetal anoxiawhich are often characterized by an erratic fetal heartbeat. Ifundetected, such disorders can cause death or brain damage to the fetus.

Heretofore, a few systems using ultrasonic energy and the Dopplerprinciple have been proposed for monitoring the fetal heartbeat. In suchsystems, a transducer passes an ultrasonic beam into the uterus of theexpectant mother where it is reflected back to the transducer. Becauseof the Doppler principle, the frequency of the reflected beam differsfrom that of the transmitted beam by an amount corresponding to thefetal heart rate motion.

A problem exists with the fetal heart monitors heretofore provided sincethey are not capable of tracking fetal heart tones for extended periodsof time without repositioning of the transducer to avoid loss of fetalheart signal. Various attempts have been made in the prior systems tospread the ultrasonic beam in order to overcome this problem. Theseattempts have included focusing methods, multitransducer configurations,and multibeam transducers focused at the same pointv None of theseefforts has been wholly successful.

Another problem encountered with fetal heart monitoring systems of theprior art is a lack of a consistent means of heart rate computation.Heretofore, it was not possible to accurately count the fetal heart rateover long periods of time because of the great variation in fetal hearttone quality.- Methods employing threshold levels, timing gates,integration and differentiation techniques have been tried with onlypartial success.

There is, therefore, a need for a new and improved fetal heartmonitoring system and method which overcome the foregoing and otherdisadvantages of the systems heretofore provided.

SUMMARY AND OBJECTS OF THE INVENTION The fetal heartbeat monitoringsystem of the present invention includes a transducer for transmittingand receiving a plurality of ultrasonic beams. The transmitting andreceiving elements in this tranducer are inclined at different angles toprovide overlapping beams of different focal lengths. This, in effect,produces a resultant beam having a focal range extending between thelongest and shortest of the focal lengths of the individual beams. Thisallows the transducer to cover a relatively large volume within theuterus. A rate computation system using frequency domain techniques isprovided for changing the fetal heart tones to a signal which describesthe fetal heart rate at any given instant. This type of rate computerhas been found to provide a significant improvement in reliabilityandease of use over time domain techniques used in the past.

It is in general an object of the present invention to provide a new andimproved fetal heart monitoring systern.

Another object of the invention is to provide a system of the abovecharacter utilizing ultrasonic and the Doppler principle.

Another object of the invention is to provide a system of the abovecharacter in which a plurality of overlapping ultrasonic beams ofdifferent focal lengths are transmitted into and received from theuterus to provide coverage of a relatively large volume.

Another object of the invention is to provide a system of the abovecharacter which includes a frequency rate computation system.

Additional objects and features of the invention will be apparent fromthe following description in which the preferred embodiment is set forthin detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of oneembodiment of a fetal heart monitoring system incorporating the presentinvention.

FIG. 2 illustrates the transducer of the system shown in FIG. I placedon the abdomen of an expectant mother.

FIG. 3 is a sectional view of a portion of the transducer, illustratingthe overlapping beam patterns produced by a pair of transducer elementsinclined at a first predetermined angle.

FIG. 4 is another sectional view, taken in a direction normal to that ofFIG. 3, of the transducer, illustrating the overlapping beam patternsproduced by a pair of transducer elements inclined at a secondpredetermined angle.

FIG. 5 is a cross-sectional view taken along line 55 in FIG. 4.

FIG. 6 is a cross-sectional view taken along line 6--6 in FIG. 4.

FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 4.

FIG. 8 is a cross-sectional view taken along line 88' in FIG. 4.

FIG. 9 is a cross-sectional view taken along line 9--9 in FIG. 4. FIG.10 is a cross-sectional view taken along line 10-10 in FIG. 4.

FIG. 11 is a cross-sectional view taken along line 11-11 in FIG. 4.

FIG. 12 is a cross-sectional view taken along line l2-12 in FIG. 4.

FIG. 13 is a block diagram of one embodiment of a frequency domain ratecomputation circuit which can be used in the system illustrated in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The fetal heartbeat detectorsystem of the present invention includes a transducer head 16, a signalgenerator or oscillator 17, a radio frequency amplifier 18, a diodedemodulator 19, an audio amplifier 21, a speaker 22, a frequency domainrate computer 60, and display devices 61 and 62.

The transducer head 16 includes a body 23 fabricated of a rigidmaterial, such as epoxy, which is formed to include a generally planarsurface 24 for placement on the outer abdominal wall of an expectantmother. The transducer head also includes a plurality of transmittingand receiving crystals which are inclined relative to the surface 24 ina manner described hereinafter in detail. In the embodiment illustratedin the drawings, four such crystals are provided, and these are disposedin diametrically opposed pairs. The first of these pairs includes atransmitting crystal 26 and a receiving crystal 27, and the second pairincludes a transmitting crystal 28 and a receiving crystal 29. Thetransmitting crystals 26, 28 are connected to the output of the signalgenerator or oscillator 17, and the receiving crystals 27, 29 areconnected to the input of the radio frequency amplifier 18.

The oscillator 17 and RF amplifier 18 are of conventional design. In thepresently preferred embodiment, the oscillator produces a sign wavehaving a frequency on the order of 2.00 megahertz, and the RF amplifierhas a pass band centered about this frequency. The RF amplifier isoperated in a linear condition. The signal received by the receivingcrystals 27, 29 and applied to the RF amplifier differs in frequencyfrom the signal produced by the oscillator by an amount corresponding.to the rate of movement of the fetal heart. The output of the RFamplifier is connected to the input of the diode demodulator 19 whichprovides means for removing the beat frequencies produced by the mixingof the frequency shifted signal reflected from the fetal heart and thetransmitter oscillator signal at the transducer, maternal interface. Theoutputof the diode demodulator is connected to the input of aconventional audio amplifier, and the output of this amplifier isapplied to a speaker 22, the frequency domain rate computer 60, and thedisplay devices 61, 62.

FIG. 2 illustrates one embodiment of a strap assembly for positioningthe transducer head 16 on the outer abdominal wall of an expectantmother. This assembly includes an adjustable belt or strap 31 forpassing around the body of the mother and an adjustable gimbal bracket32 for holding the planar surface of the transducer head against theouter abdominal wall. Since the gimbal bracket is adjustable, the planarsurface of the transducer head can be moved to any desired anglerelative to the abdominal wall without disturbing the remainder of thestrap assembly.

The transmitting and receiving crystals 26, 27 are inclined relative tothe planar surface 24 of the transducer head by an angle which in thepreferred embodiment has magnitude on the order of 4. The crystals 28,29 are inclined relative to the planar surface by an angle if) having amagnitude on the order of 6. The beam patterns produced by thetransmitting and receiving crystals are illustrated in FIGS. 3-12, withthe beams produced by the crystals 26 and 27 being designated by thereference numerals 26T and 27R, respectively and the beams produced bythe crystals 28 and 29 designated by the reference numerals 2ST and 29R,respectively. While the beams are illustrated as having circular crosssections, they may have any other desired shape, this shape beingdetermined by the shape of the crystals.

As the distance from the planar surface 34 increases, the beams 26T-29Rconverge, cross over, and then diverge from each other. The beams 28Tand 29R cross over in a plane 36, producing a first focus. Thecrosssectional view 8-8 is taken along this plane and illustrates thefirst cross-over point. The beams 26T, 27R cross over in a plane 37 toproduce a second focus. The cross-sectional view 9-9 is taken throughthe plane 37. With the crystals inclined at angles on the order of 4 and6 degrees, the plane 36 is spaced from the planar surface 24 by adistance on the order of 16 centimeters, and the plane 37 is spaced adistance on the order of 24 centimeters from this surface. Thesedistances would be somewhat less but for a slight defraction which isproduced by the epoxy which covers the crystals.

The beams 26T-29R are not well defined, and therefore the two foci mergeinto each other, producing an elongated focus which extends from lessthan 16 centimeters to more than 24 centimeters. Also, it should benoted that the beams 26T-29R overlap and cross each other in more thanthe two planes 36, 37 thus enabling the transducer to be sensitive to arelatively large volume within the uterus.

While the presently preferred embodiment of the invention utilizes twopairs of transmitting and receiving crystals, other numbers of crystalscan be used to provide the elongated focus effect. Thus, for example,three crystals would likewise produce satisfactory results in thesystem. Similarly, the 4 and 6 angles are not critical, and other anglescan be used if desired.

The frequency domain rate meter illustrated in FIG. 13 includes anautomatic gain control circuit 41, whose gain iscontrolled by theamplitude of the incoming fetal heart sound signal emanating from thedoppler fetal heart tone detector. Following this circuit appears afrequency translation system comprising a diode demodulator 42, whichhalf wave rectifies the amplitude stabilized doppler heart tone signal,and translates the frequency components of this signal such that theyappear around a 0 Hz center frequency, rather than around a fundamentalfrequency that may vary between l50 Hz to 1500 Hz. A 1.12 Hz to 3.25 Hzlow frequency band pass filter, 43, removes all the associated upperside bands of the demodulated fetal heart tone signal and passes onlythe first side band, the fetal heart rate component. This signal is fedto a zero crossing detector 44, which produces a pulse for every cycle.In order to translate this pulsed information to a DC level to drive adigital voltmeter and/or a graphic strip chart recorder, a beat-to-beatcounter 45, is provided. This device functions as a pulse to DC levelcounter, translating, on an instantaneous basis, the pulsed informationto a voltage amplitude which is directly proportional to the fetal heartrate frequency. The output of the system is in units of beats perminute.

Operation and use of the fetal heart beat monitoring system can now bedescribed briefly. Let it be assumed that the transducer head 16 hasbeen placed on the outer abdominal wall of the expectant mother in themanner illustrated in FIG. 2. Ultrasonic or RF energy having a frequencyon the order of 2 Megahertz is em itted into the uterus or womb of theexpectant mother through the transmitting crystals 26, 28. This energyis reflected off the fetus and the walls of the uterus and is returnedto the receiving crystals 27, 29 at a frequency differing from theoscillator frequency by an amount corresponding to the velocity of thefetal heart motion. The received signal is amplified by the RF amplifierand applied to the diode demodulator 19. The output of the diodedemodulator is a signal having a frequency corresponding to thefrequency of the fetal heartbeat and a magnitude corresponding to thestrength ofthe heartbeat. This signal is amplified in the audioamplifier 21 and applied to the speaker 22 and frequency domain ratemeter 60, where the heart rate is extracted and displayed in the form ofa line on a graph or as a direct reading digital output.

The method of the present invention should be apparent from theforegoing description of the apparatus. Briefly, this method can besummarized as including the steps of transmitting a signal having apredetermined frequency into the womb of an expectant mother in suchmanner that the signal is reflected by the fetal heart, the reflectedsignal having a frequency differing from the transmitted signal by anamount corresponding to the rate of the fetal heart movement, receivingthe reflected signal, and comparing the frequency of the received signalwith that of the transmitted signal to determine a doppler heart tonesignal which is subsequently impressed on a rate computer of uniqueembodiment in order to extract the fetal heart rate from thisconglomerate signal. The signals are transmitted and received by aplurality of transducer elements inclined at different angles relativeto the outer abdominal wall of the expectant mother.

From the foregoing, it is apparent that a new and improved method andapparatus have been provided for monitoring fetal heartbeats. Thissystem makes it possible to track such heartbeats for extended periodsof time, and it has been found to provide reliable tracking for periodsin excess of twelve hours without need for repositioning the transducerhead. The signal tracked does not have to come directly from theperticardium of the fetal heart, butcan come from other sources such asthe heart valves or the flow of fetal blood across the placenta. Whileonly one presently preferred embodiment of the invention has beendescribed herein, as will be apparent to those familiar with the art,certain changes and modifications can be made without departing from thescope ofthe invention as defined by the following claims.

I claim:

1. In a system for monitoring the heart-beat of a'fetus in the womb ofan expectant mother, a transducer assembly including a generally planarsurface, strap means for holding the assembly in a predeterminedposition on the outer abdominal wall of an expectant mother, saidtransducer assembly including a plurality of transducer elements mountedin a single plane and inclined at predetermined angles relative to thegenerally planar surface for transmitting energy into the womb of theexpectant mother and receiving energy reflected from within the womb indiscrete beams, said beams intersecting each other in an elongatedregion extending along an axis normal to the planar surface, thereflected energy having a fetal heart rate component which differs infrequency from the transmitted energy by an amount corresponding to therate of fetal heart movement, signal generating means connected to someof said transducer elements, and means connected to others of saidtransducer elements for processing signals received thereby to recoverthe fetal heart rate component of said signals.

2. A system as in claim 1 wherein said transducer elements are providedin pairs, each of said pairs including one transmitting element and onereceiving element, the elements in different pairs being inclined atdifferent angles relative to said generally planar surface so that thebeams associated with different pairs intersect along the axis atdifferent distances from the generally planar surface.

3. A system as in claim 1 together with means for converting the fetalheart rate component to an analog signal.

4. A system as in claim 1 together wih controlled gain amplifier meansfor amplifying the reflected signal.

5. A system as in claim 1 wherein the means for processing the receivedsignals includes means for translating the frequency of the reflectedsignal so that said signal has a predetermined center frequency,bandpass filter means for separating the fetal heart rate component fromthe remainder of the frequency translated signal, and means forconverting the fetal heart rate component to a pulsating signal.

1. In a system for monitoring the heart-beat of a fetus in the womb ofan expectant mother, a transducer assembly including a generally planarsurface, strap means for holding the assembly in a predeterminedposition on the outer abdominal wall of an expectant mother, saidtransducer assembly including a plurality of transducer elements mountedin a single plane and inclined at predetermined angles relative to thegenerally planar surface for transmitting energy into the womb of theexpectant mother and receiving energy reflected from within the womb indiscrete beams, said beams intersecting each other in an elongatedregion extending along an axis normal to the planar surface, thereflected energy having a fetal heart rate component which differs infrequency from the transmitted energy by an amount corresponding to therate of fetal heart movement, signal generating means connected to someof said transducer elements, and means connected to others of saidtransducer elements for processing signals received thereby to recoverthe fetal heart rate component of said signals.
 2. A system as in claim1 wherein said transducer elements are provided in pairs, each of saidpairs including one transmitting element and one receiving element, theelements in different pairs being inclined at different angles relativeto said generally planar surface so that the beams associated withdifferent pairs intersect along the axis at different distances from thegenerally planar surface.
 3. A system as in claim 1 together with meansfor converting the fetal heart rate component to an analog signal.
 4. Asystem as in claim 1 together wih controlled gain amplifier means foramplifying the reflected signal.
 5. A system as in claim 1 wherein themeans for processing the received signals includes means for translatingthe frequency of the reflected signal so that said signal has apredetermined center frequency, bandpass filter means for separating thefetal heart rate component from the remainder of the frequencytranslated signal, and means for converting the fetal heart ratecomponent to a pulsating signal.